<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>全网页设置灰色</title>
  <style>
    html {
      filter: grayscale(1);
    }
  </style>
</head>
<body>
<iframe src="https://lol.qq.com/" width="100%" height="5000px"></iframe>
</body>
</html>